Machines are commercially available for sealing packaging boxes by automatically applying adhesive tape, commonly known as "packaging machines". A machine of this type, of relatively simple structure, comprises essentially a bed incorporating conveying means for feeding the boxes to be sealed, and/or means for applying the adhesive tape, and a pair of uprights projecting upwards from the bed and supporting a working head which operates downwards on the boxes and which also comprises conveying means and/or means for applying the adhesive tape.
Normally, the bed is formed from a rectangular main frame comprising a central space for housing self-contained, self-supporting, work units-for example and conveying and/or taping units, already mounted on their own support frame-and having slide roller mounted laterally. Uprights are also fixed to the frame sidepieces and project upwards to support the upper working head.
Such a construction is not generally satisfactory because:
if repair or maintenance work has to be carried out on the central conveying and/or taping unit, this unit has to be completely removed from the frame and remounted after repair; PA0 the main frame is subjected to considerable loads, including moving loads, so that it easily undergoes torsional bending, particularly when it does not rest perfectly flat on the floor.
In an attempt to obviate at least part of these drawbacks, it has already been proposed to mount the conveying and/or taping unit not on the frame sidepieces, as in the known art, but on brackets projecting from the frame endpieces, so as to leave a free space to the sides of said unit, this space being covered by removable plates.
This emthod has the advantage of facilitating at least one of the maintenance operations, i.e. the replacement of the wearable conveyor belts-when these are of the endless type-by drawing them out frm the open sides and thus without removing the head. This method is not however free from complications as it requires removable plates to be used instead of lateral slide rollers, with obvious increase in friction, and it also further overloads the frame through the weight of the end support brackets.
Moreover, it does not solve all the other maintenance and/or repair problems, for which it is still essential to remove the head from the frame, neither does it solve the problems deriving from the poor frame rigidity, and if anything aggravates them.
However, in order to solve these problems of frame resistance to torsional stresses, there is currently no other way than to construct the frame of thicker and stronger iron sections, obviously to the detriment of the lightness and manageability of the entire machine, and increasing its cost.